For 2010, variable valve timing has been added to the 4.8-liter and 5.3-liter engines.All the V8 engines have Flex Fuel capability (meaning they will run on E85).A 3.08:1 axle ratio and fuel saver mode is standard with the 5.3-liter V8 for improved fuel economy, and a six-speed automatic transmission comes on Regular and Extended Cab models with the 5.3-liter V8.The 6.2-liter V8 is available for Sierra Extended Cab and Crew Cab models, and is useful for towing heavier loads.

The Sierra Hybrid uses GM's Two-Mode Hybrid system.It's available only as a Crew Cab model with a specially tuned 332-horsepower 6.0-liter V8 working in conjunction with a battery pack and a four-speed automatic transmission that houses two electric motors.The Hybrid is EPA-rated at 21 mpg City/22 mpg Highway, while compromising payload and towing capacity (maximum around 6000 pounds).

A choice of interior styles is available.The traditional layout, called pure pickup, has a driver-oriented dash layout with large switchgear and door handles designed for work gloves.The pure pickup interior includes a 40/20/40 split front bench seat with the center section folding down to provide a large storage compartment and wide armrest.

The luxurious Sierra SLT has a cabin similar to that of a luxury SUV, with two front bucket seats separated by a fixed center console.This design places audio and ventilation system controls more easily within reach of the front-seat passenger, who may or may not be a spouse, and it offers space for a navigation system and storage compartments.

The Sierra Denali makes for a comfortable, luxurious pickup with the emphasis on performance rather than payload and towing capacity.The Sierra Denali offers the same sort of high-line content as the upscale GMC Yukon Denali sport utility, and it's available with all-wheel drive.Denali comes with a 6.2-liter V8.

For 2010, side-curtain airbags and seat-mounted side airbags are standard.USB connectivity is provided in the center console of all 2010 Sierra models, and availability of the rearview camera has been increased.StabiliTrak electronic stability control with rollover mitigation is standard on all 2010 Sierra 1500 models.

The 5.3-liter V8 provided plenty of power for the extended cab SLE models we drove.All engines need to be revved up (by truck standards) for best performance.Generally, the Sierra models match competitors for smoothness.

Of the suspensions, the Z83 is claimed the smoothest ride.The Z85 is slightly stiffer and for those who often tow moderate trailers, a good choice for towing.The Z71 is set up to enhance off-pavement driving yet works very well on the road.In fact, we think the Z71 is the best suspension setup for comfort on the widest range of surfaces.The Z60 configuration is for street performance and includes big 20-inch wheels; we like performance but think trucks should be trucks, so the Z60 is not our first choice.The NHT Max Trailering Package is designed for Sierra owners who need to tow and carry the heaviest loads.

With NHT, the SLT Crew Cab 4x2 is equipped with the 6.2-liter V8 engine.The SLT with NHT suspension is designed for maximum capacity trailer towing, with a special steering gear, shock absorbers, rear axle and tires.We found the NHT suspension compliant relative to its carrying capacity.Isolation and control are both very good.By virtue of its fairly stiff spring and shock rates, the NHT suspension can be driven aggressively on winding roads with tire squeal the primary indication you're approaching the cornering limits.Steering is direct by truck standards and nicely weighted, providing good feedback about how hard everything is working, though the assist can fall behind during repeated full-lock maneuvering as when backing a trailer.However, if you mostly use the truck with it empty and don't often tow, we don't recommend the NHT package, due to its harsher ride.

The integrated brake controller should find favor with drivers who tow RV or box trailers.However, be sure your trailer brakes are compatible with it before choosing the option, as some electro-hydraulic disc conversions do not work with the integrated controller.If it is compatible, it's a great feature, eliminating the mess of installing an aftermarket unit and offering more precise braking.

The highest tow rating for a Sierra is 10,700 pounds on Extended Cab (not long bed) or Crew Cab model; top Regular Cab rating is 10,000 pounds.Note these figures typically apply to a truck with just a driver on board, and vary substantially based on a variety of equipment and options.

G.R.Whale test drove various Sierra models and filed this report to NewCarTestDrive.com from California; with Larry Edsall reporting from Phoenix.

The pure pickup, as it's called, has a unique dashboard that is more driver-oriented and has large switchgear and door handles that are designed to be easily manipulated by those wearing work gloves.The pure pickup interior includes a 40/20/40 split front bench seat with the center section folding down to provide a large storage compartment and wide armrest.

The SLT's SUV-style luxury-oriented interior puts audio and ventilation system controls more easily within reach of the front-seat passenger and has two front bucket seats with a fixed center console with assorted storage compartments.

Either dashboard sports full analog instrumentation, and may have more information available through digital display.Operating controls are GM simple, especially on the pure pickup, while on the top-line models the central dash has many small white-on-black buttons that may require a short learning curve.Some drivers report peculiar ergonomic details as the steering wheel is slightly offset from the seat centerline (which is not uncommon).

Rear seating is provided for three people in the Extended and Crew Cab versions; with 34.3 inches of rear legroom in the Extended Cab and 39.0 in the Crew Cab, space is similar to Ford's F-150 and Nissan's Titan, and smaller than Dodge's Quad and Mega Cabs and Tundra's Double and CrewMax cabs.The Crew Cab rear seat is split 60/40 and can folded up individually for a flat load floor; this arrangement is optional on extended cabs.

Access to the rear seating area of the Extended Cab is eased by rear-hinged doors that open to nearly flush with the bed sides.Sitting in the back seat of the Extended Cab is made more pleasant thanks to the fact that the windows in the rear access doors power fully down.

The Regular Cab is designed for fleet buyers and others who want a basic truck for work, budget play, or a clean slate for customization.It can be equipped with a standard bed (6-foot, 6-inch) or a long bed (8-foot), two bucket seats or a three-person bench seat, V6 or V8 engines.

The Extended Cab has two rows of seats with rear-hinged rear access doors that open 170 degrees and have roll-down windows.The Extended Cab can be equipped with a short (5-foot, 8-inch), standard or long cargo bed, and with seating for five or six people.

The Crew Cab has two rows of seats and four front-hinged doors.It can be equipped with seating for five or six and comes with the short bed.

Standard equipment on the basic Work Truck ($20,850) includes vinyl seating surfaces, air conditioning, AM/FM/XM radio, daytime running lights, tire pressure monitoring system, Smooth Ride suspension, 17-inch wheels, and chrome bumpers.The 4.6-liter V6 engine is standard.

Sierra SL ($28,340-$33,715) is available in Extended Cab and Crew Cab trim levels, and adds a CD player with MP3 capability, deep tinted glass, OnStar, chrome grille surround, body-side moldings, styled steel wheels, cruise control, remote keyless entry, cloth upholstery, and power mirrors, windows and door locks.The 4.8-liter V8 is standard.

Sierra SLE ($27,225-$35,025) adds premium cloth upholstery, auto-dimming rearview mirror with compass and outside temperatures, leather-wrapped steering wheel, handling/trailering suspension, carpeting, a six-speaker audio system, illuminated visor vanity mirrors, and alloy wheels.Available options include dual-zone air conditioning, a floor console, power driver and front passenger seats, audio controls on the steering wheel, and machined aluminum wheels.

Sierra SLT ($35,780-$42,275) adds leather seat trim, a unique instrument panel, upgraded audio system with Bose premium speakers, heated windshield washers, Bluetooth, front bucket seats with 10-way power adjustment and heat, fog lamps, dual-zone climate control, rear window defogger, remote start, polished aluminum wheels, and the 5.3-liter V8 engine.Crew Cab models also get a rear-seat audio system.

Sierra Denali ($43,285) includes a top-flight interior with leather, unique woodgrain console, park assist and the standard luxury and convenience features from the preceding trim levels.The options include a heated steering wheel, heated/cooled front seats, sunroof, and rear-seat entertainment.The Denali comes only as a Crew Cab with the 403-horsepower 6.2-liter V8 engine, six-speed automatic transmission and rear or all-wheel drive.

Sierra Hybrid, available as a Crew Cab only, uses a 332-horsepower 6.0-liter V8 in conjunction with a battery pack and four-speed automatic transmission that houses two electric motor units.With EPA ratings in the 21-22 mpg range its urban economy is the best of the Sierras, the compromises being price, payload (maximum in the mid-1400-pound range) and maximum towing capacity around 6000 pounds.

Options include a locking rear differential, towing and trailering equipment, and a power sunroof.

Safety features include dual front airbags, head-curtain airbags that automatically inflate when sensors sense a severe impact to provide extra protection in the event of a rollover or secondary collision, driver and front-seat passenger side-impact air bags, anti-lock brakes, StabiliTrak electronic stability control with rollover mitigation technology, and tire-pressure monitoring.The optional Autotrac active transfer case, ultrasonic rear park assist, and OnStar emergency notification can further enhance safety, as can the all-wheel-drive system on the Denali.

Top trim levels get some distinguishing features.The Denali gets its own chromed grilles, both the upper section and the air vent below the front bumper, and the bumpers are painted to match.Hybrid models are festooned with odd-looking H badges.

The Sierra hood has a pair of long, narrow V-shaped power bulges and leads back to a steeply raked windshield.The windshield is tilted back for improved aerodynamics and enhanced highway fuel economy.

The side view features slightly bulging and elongated fender flares that sweep down behind the headlamps.The sides of the cargo bed are higher than on previous models, and the exterior of the tailgate is sculpted, enhancing the rear view of the truck.Stacked tail lamps are on either side of the tailgate.

A cargo management system is available for the bed with side rails and various cargo-carrying and cargo-controlling boxes and dividers and tie-downs.

The GMC Sierra and Chevy Silverado are built on the GMT900 platform that debuted in 2007 and shares many underpinnings with the Yukon, Suburban, and Tahoe SUVs.The pickups get a unique rear suspension and stiffer rear frame section.The Sierra and Silverado share mechanical components, with the exception of the unique features found on the Sierra Denali.

Compared with the previous-generation models, the current frame is much stiffer in all directions.This stiffness contributes to a smoother ride and better handling.It also allowed the engineers to reduce the gap between the truck bed and passenger compartment as well as the gaps between fenders and bumpers, all of which enhances aerodynamics and fuel efficiency.

The front suspension uses a coil-over-shock setup and the rack-and-pinion steering gear is mounted to the engine cross-member frame.The truck also has a rear axle design with shock absorbers mounted outboard and more upright for better dynamic control.

Except for Hybrids, EPA ratings run 13-15 mpg City, 19-22 mpg Highway, and on E85 those numbers drop substantially.The XFE (Xtra Fuel Economy) models with a 5.3-liter V8, six-speed automatic and axle ratio of 3.08:1 increase EPA ratings form 15/21 to 15/22.Proprietary XFE pieces include aerodynamic upgrades in the form of a soft bed cover and extended front air dam, plus aluminum wheels (including the spare) and lower front suspension arms, locking rear differential, and low rolling resistance tires.A trailering package is standard so XFE models can tow up to 7000 pounds.